This core will assess surfactant metabolism a and surfactant function in the normal and transgenic mouse models used for the projects. All techniques to be used in this Core have been previously published in studies using transgenic mice. Four techniques to be used in this core have been previously published in studies using transgenic mice. Four types of measurements of surfactant metabolism and function will be provided to the projects: 1. Metabolic measurements of surfactant in vivo will include a) pool sizes of saturated phosphatidylcholine (Sat PC) in alveolar lavage and lung tissue; b) phospholipid composition for selected studies; c) radiolabeled precursor incorporation into St PC and measurements of the kinetics of surfactant secretion; and d) clearance kinetics for radiolabeled surfactant components (Sat PC, SP-A, SP-B, SP-C) given by intratracheal injection. These measurements provide information on the flux of surfactant into and out of the alveolus. 2. The surface activity of surfactant will be evaluated in vitro by measurements of a) minimum and maximum surface tension: b) sensitivity of surface tension lowering properties of surfactant to inhibition by plasma protein; and c) absorption rate. The Wilhelmy balance and/or captive bubble surfactometer will be used for above measurements. 3. Surfactant function will be measured in vivo by giving surfactant isolated from alveolar laves of mice to be surfactant deficient 27 d gestation premature rabbits. The effects of the test surfactants on dynamic compliance during ventilation and static pressure volume curves of the premature rabbit lung will be quantified.